Throughout the world, human activity has resulted in many polluted sites, which are contaminated by organic compounds. Usually, such contamination results where organic compounds can seep into the environment, e.g. into the water and/or soil (ground or sediment), which thus become contaminated by the organic compounds (“environmental pollution”). Unfortunately, the presence of organic compounds as environmental pollutants is not restricted to sites of present or past industrial activity, but may also occur in places of accidental or deliberate release. For example, accidental spills may occur during transport or storage of organic compounds, e.g. by accidental damage of transport vehicles or devices (such as tankers or pipelines) or of transport or storage containers, which might be caused by human action, natural disaster (e.g. earthquake or fire), or disintegration (e.g. by corrosion), or the like, but also because of improper or sloppy handling or disposal, e.g. by utilising unsuitable containers.
The predominant organic compounds found in contaminated sites are hydrocarbon compounds, both aliphatic and aromatic hydrocarbons. Possible sources of such hydrocarbon compounds are, for example, products derived from crude oil, such as petrol, diesel, tar etc. Examples of these hydrocarbon compounds may be liquids themselves, or compositions containing both liquid components and solid components dissolved therein, so that they may seep into the soil and/or groundwater. The overall mobility of such compounds is usually dependent of external factors, such as, the ambient temperature at the site, etc. Moreover, the seeping of hydrocarbon compounds into the soil can be assisted by water flow, for example, by rain or surface water. Once inside the soil, the organic compounds can spread further and may eventually arrive in the groundwater, where further spreading of the pollutant can be assisted by the natural flow within the aquifer, leading to a progressing spreading of the pollution. Since even very small amounts of hydrocarbons can contaminate large amounts of water, which is then unsuitable for consumption by living organisms, such as plants, animals or humans, water and/or soil contaminated with hydrocarbons has to be expensively treated in order to become suitable for consumption.
A common way of treatment is the excavation of contaminated soil, which is then decontaminated off-site. This method requires that large amounts of contaminated soil are moved and subsequently treated (decontaminated). However, if a contamination is not detected immediately and could thus spread, the shear amount of contaminated soil may require the removal of so much soil that the excavation method becomes impractical. And even if the most polluted volume of soil comprising the original source of pollution could be removed, the residual pollutants having spread to adjacent sites might still require the treatment of huge volumes of soil.
Moreover, the contamination might not be accessible from the surface at all, for example, in cases of subsurface sites where the primary source of pollution originates in or below a building (e.g. in case of a leaking fuel oil tank integrated in a building), or in cases where the contamination has spread underneath a structure, such as a building, a street, or the like. Or the pollution might threaten to spread into a sensitive subsurface area, such as, e.g. an aquifer used for water consumption. In such cases, in addition to the removal of the primary source of contamination, it might become necessary to restrict further spreading of the contamination by construing a barrier. One possibility for forming a barrier is the digging of trenches and/or the introduction of impenetrable materials, which, however, might not always be possible for reasons of site accessibility and/or costs.
So far, several methods for the in situ (on-site) remediation of contaminated sites have been developed wherein the polluted sites are treated with various compounds. However, especially in cases of sensitive subsurface sites, such as aquifers used for water consumption, the water protection laws of most countries strongly restrict the nature of compounds which may be used for on-site treatment.
One known method utilises nanoscale metal particles, such as colloidal suspensions of nanoscale metallic particles, which are directly pumped into polluted subsurface sites, where they enhance the reductive dehalogenation of halogenated hydrocarbons. Especially, suspensions of nanoscale particles comprising metallic iron, which is considered to be no hazard to sensitive sites, are used for the in situ remediation of sites polluted with halogenated hydrocarbons, as described, for example by W. Zhang in Journal of Nanoparticle Research 5: 323-332, 2003. A method of making and using nanoscale metal for the in situ environmental remediation of chlorinated solvents is also described in U.S. Pat. No. 6,777,449 B2 and U.S. Pat. No. 7,301,066 B2. These methods are suitable for the reductive dehalogenation of halogenated hydrocarbons, but not for the remediation of sites polluted with hydrocarbons which cannot be degraded by reductive means, such as, for example, aliphatic hydrocarbons. Moreover, U.S. Pat. No. 5,857,810 A1 describes the use of a suspension of solid particles including metallic iron colloids for the formation of an in-situ chemical barrier. However, these chemical methods rely on the reductive degradation of pollutants, such as halogenated hydrocarbons, by using metallic reagents, such as iron metal, which are highly sensitive against oxidative degradation themselves. Thus, these methods might require to introduce large amounts of the respective metallic reagents into the sites to be treated. Moreover, they also result in hydrocarbon compounds which can be considered pollutants too. Additional to these methods for the reductive degradation of pollutants, U.S. Pat. No. 5,741,427 A1 describes a method for the in situ remediation of soil and/or groundwater by adding an oxidizing agent and a metal catalyst. However, owing to the unfavourable electron balance, this chemical method also requires the use of large amounts of the respective compounds to be brought into the sites to be treated, thus increasing its costs.
It is known that certain indigenous micro-organisms are capable of the oxidative degradation of hydrocarbon pollutants under anaerobic conditions. For example, the ubiquitous bacteria Geobacter sulfurreducens, Geobacter Grbiciae, Shewanella alga, Shewanella putrefaciens, and the like are known to accumulate at sites of hydrocarbon contamination, as they can use aliphatic or aromatic hydrocarbon compounds as carbon sources under anaerobic conditions. It is also known that these bacteria can use ferric iron oxides, which are usually present in the soil or sediment matrix, as a respiratory equivalent (electron acceptor) under anaerobic conditions (cf. e.g. E. E. Roden and J. M. Zachara, Environ. Sci. Technol. 1996, 30, 1618-1628). However, the biological or bacterial degradation of pollutants usually occurs on a very slow time scale. This seems to be caused by the limited accessibility of the iron oxide minerals which are generally insoluble under environmental conditions.
Therefore, it is an object of the present invention to provide a method for the biological remediation of polluted sites, wherein the method should be versatile, universally applicable, easy to use and cost-efficient, without requiring to further strain the already polluted environment. Moreover, it is another object of the present invention to provide a method for forming a barrier against the further spreading of a contamination. Finally, it is an object of the invention to provide the means for use in these methods and for the production of such means.